Field of the Invention
The present invention relates to a joint compound for use in filling and coating the joints between adjacent gypsum wallboards, and more particularly refers to a joint compound of the type described which has a lighter weight and better sandability than conventional joint compounds thereby reducing transportation costs, facilitating the handling of containers and application tools and facilitating the final sanding and finishing of the wallboard joints.
In the construction of buildings, one of the most common elements is gypsum wallboard, often known as "drywall," used to construct the walls and/or ceilings. Walls made from gypsum wallboard are conventionally constructed by affixing the panels to studs or joints and filling and coating the joints with a specially prepared adhesive called a "joint compound." This process generally proceeds in the following fashion: a taping grade joint compound is placed within the joint formed by the abutted edges of the wallboards, and a liquid-permeable tape is embedded within the taping compound. When dry (or set), a second coating comprising a topping grade joint compound is applied over the joint. This may be sanded lightly, and then a third coat applied and conventionally finished. Another grade of joint compound is an all-purpose grade which may be used, as the name suggests, both for embedding the tape and for applying as finishing coats. In some instances, a patterned effect is given to the finished wall and joint with the all-purpose joint compound to provide a textured finish.
The primary difference in the past between the various grades of joint compound has been in the differences in the amounts of each ingredient. Thus, no matter what the grade, joint compounds invariably include a filler, and a binder. More binder is used for the taping grade than for the topping grade. Typical fillers may be calcium carbonate, calcium sulfate hemihydrate, or calcium sulfate dihydrate. As is obvious, the choice determines whether the joint compound hardens by drying or by setting. An example of a setting type joint compound is taught in U.S. Pat. No. 3,297,601.
In U.S. Pat. No. Re. 29,753 joint compounds are disclosed which are free of asbestos and utilize attapulgus clay to provide the non-leveling properties previously obtained by the use of asbestos fibers. Conventional compounds with or without attapulgus clay have proven to be excellent. However, they are quite heavy and expensive to transport. Additionally, when the conventional joint compounds dry, they have a hard texture and are difficult to sand in order to provide the joint treatment with a smooth surface. It would be desirable to have a joint compound which is of lighter weight than conventional joint compounds and which, when dry can be readily sanded to provide a smooth surface.